Astronomy and Astrophysics – Astrophysics
Scientific paper
May 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002a%26a...386.1123s&link_type=abstract
Astronomy and Astrophysics, v.386, p.1123-1128 (2002)
Astronomy and Astrophysics
Astrophysics
9
Sun: Oscillations, Magnetic Fields, Sunspots, Instrumentation: Interferometers, Techniques: Spectroscopic, Polarimetric
Scientific paper
We will show the potential errors of observations using instruments, where a line spectrum is obtained not instantly but by scanning through the spectral line in time. We give two examples in simulations of a sunspot observation with the measuring procedure of a typical Fabry-Perot interferometer (FPI) spectrometer and the Michelson Doppler Imager (MDI) on board of the Solar and Heliospheric Observatory (SOHO). The effect described is inherent for observations with a low intensity input signal, where the accumulation time for one image and therefore the whole process of measuring a spectrum is relatively high compared to the timescale of the underlying physical processes. We show that our simulated data produce an error in magnetic field strength and - in a time series - result in an apparent oscillation of the magnetic field strength, while the input contained only velocity oscillations. As the FPI spectrometer is being used more and more widely, one has to be aware of the disadvantages and potential errors when interpreting its data. We encourage every observer to do the simple simulation as described for every specific setup used.
Carroll Andrew T.
Nickelt Iliya
Norton Andrew
Settele A.
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